De novo formation characteristics of dioxins in the dry zone of an iron ore sintering bed

A review of hydrogen chloride removal from calcium- and sodium-based sorbents

With the steady progress of ultra-low emissions in various industries, the management of unconventional pollutants is gradually attracting attention. A such unconventional pollutant that negatively affects many different processes and pieces of equipment is hydrogen chloride (HCl). Although it has strong advantages and potential in the treatment of industrial waste gas and synthesis gas, the process technology of removing HCl by calcium- and sodium-based alkaline powder has not yet been thoroughly studied. The impact of reaction factors on the dechlorination of calcium- and sodium-based sorbents is reviewed, including temperature, particle size, and water form. The most recent developments in sodium- and calcium-based sorbents for capturing hydrogen chloride were presented, and the dechlorination capabilities of various sorbents were contrasted. In the low-temperature range, sodium-based sorbents had a stronger dechlorination impact than calcium-based sorbents. Surface chemical reactions and product layer diffusion between solid sorbents and gases are crucial mechanisms. Meanwhile, the effect of the competitive behavior of SO₂ and CO₂ with HCl on the dechlorination performance has been taken into account. The mechanism and necessity of selective hydrogen chloride removal are also provided and discussed, and future research directions are pointed out to provide the theoretical basis and technical reference for future industrial practical applications.

Emission characteristics of dioxins during iron ore Co-sintering with municipal solid waste incinerator fly ash in a sintering pot

The disposing of municipal solid waste incineration(MSWI) fly ashes containing dioxins is an intractable problems. Co-sintering is one of the most ideal methods to dispose MSWI fly ash, because it not only degrades the dioxins but also makes it possible to re-utilize MSWI fly ashes. In the present study, MSWI fly ash(FA) and water washed MSWI fly ash(WFA) were added into the sinter raw mixture in a lab-scale sintering pot. Different effects of fly ash and water washed fly ash on emission characteristics of dioxins were studied, and possible pathways to form dioxins were discussed in detail. During co-sintering, at least 88.9%, 99.1% of dioxins brought in by FA, WFA was decomposed, respectively, and re-synthesis with a significant distribution characteristic of dioxins originated from sintering process. In the preheating and dry zone, the recombination and condensation reaction of precursors were the main formation pathways of 2,3,7,8-PCDDs in the sintering process and 2,3,7,8-PCDFs were formed by de novo synthesis. In addition, the resynthesis process was affected by chlorine and calcium brought in by fly ash. Sufficient chlorine boosted the chlorination of reactants while calcium increased the residence time, causing the emission concentration of toxic dioxins and the adding ratio were nonlinearly dependent. Therefore, the maximum proportion of water washed MSWI fly ash that can be added into the sintering process was 0.5 wt.%. Besides, the possible pathways to form dioxins were proposed.

Occurrence, profiles, and control of unintentional POPs in the steelmaking industry: A review

The steelmaking industry is an important source of unintentionally produced persistent organic pollutants (UP-POPs). This review summarizes the emission levels, characteristics, and formation mechanisms of UP-POPs, including halogenated dioxins, polychlorinated biphenyls, polychlorinated naphthalenes, and penta- and hexa- chlorobenzenes in the steelmaking industry to improve our understanding of the emissions of UP-POPs from the steelmaking industry. The factors influencing UP-POP formation during the iron ore sintering (IOS) process are also reviewed. The raw materials and temperature during the steelmaking process are important factors influencing UP-POP generation. Raw materials containing plastics, paints, cutting oil, rubber, and iron from electronic waste recycling can contribute to high emissions of UP-POPs during steelmaking processes. Electrostatic precipitator dust contains chlorine, carbon, and metals, which are usually recycled as a component of the raw material, and could also promote dioxin formation and emissions from IOS. Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) are easily formed in high concentrations at temperatures in the range of 200 °C-650 °C. This review also provides a comprehensive summary of the UP-POP emission limits in the steel industry worldwide and the best available techniques and environmental practices for UP-POP emission reduction. The information in this review will be useful for the reduction of UP-POPs in the steelmaking process.

Incineration experiment of medical waste of novel coronavirus pneumonia (COVID-19) in a mobile animal carcass incinerator

Incineration experiment of medical waste was carried out in a mobile animal carcass incinerator. Simulated medical waste (69% cotton, 1.5% wood product, 4.5% mask and 25% moisture) was used as raw material. The temperature trend of first and second combustion chamber, the operating conditions and the emission characteristics of gaseous pollutants were studied. The results indicated that the temperature of first combustion chamber can be maintained at 550-650 °C without external heating, while in the final stage a burner was used to realize the burnout of material. The temperature of the second combustion chamber was always lower than that of the first combustion after the burner stopped working. The concentration of CO emission in flue gas was high due to the low disposal efficiency of the mobile incinerator, while NO_X and SO₂ emission concentrations were far below the standard limit value (GB 18484-2001).

The bibliometric analysis and review of dioxin in waste incineration and steel sintering

Facing the common treatment problems of dioxin whose major sources come from waste incineration and steel sintering, we handled a massive literature dataset from the Web of Science database and analyzed the research hotspot and development trend in this field in the past 40 years by bibliometric method. The result indicates that the field of dioxins generated from waste incineration and steel sintering has entered a stage of rapid development since 1990. China occupies a leading position in terms of comprehensive strength with the largest publications output as well as a greater influence in recent years. The most productive institutions and journals are Zhejiang University and Chemosphere, respectively. In addition, the most commonly used keywords in statistical analysis are "fly ash," "emission control," "risk assessment," "congener profile," "formation mechanisms," "sources," "catalysis," and "inhibition," which reflects the current main research direction in this field. The similarities and differences of dioxins generated in waste incineration and steel sintering are reviewed in this paper, which will provide guidance for the future research.

Application of national pollutant inventories for monitoring trends on dioxin emissions from stationary industrial sources in Australia, Canada and European Union

Industrial sources, including iron ore sintering, municipal waste incineration and non-ferrous metal processing have been prominent emitters of dioxins to the environment. With the expanding industrial sectors, many international conventions were established in order to reduce the emission of dioxins in the past two decades. The Stockholm convention, a global monitoring treaty, entered into force in 2004 with the aim to promote development of strategies to reduce or eliminate dioxin emissions. According to the convention, parties are required to develop national inventory databases to report emission levels and develop a national implementation plan (NIP) to reduce further dioxin emissions. In order to understand the trend of dioxin emissions since 1990s this study provides a comparative assessment of dioxin emissions from different industrial sources by deriving emission data from the national inventory databases of Australia, Canada and the 28 European countries (EU-28). According to the data collected, iron and steel production and electricity generation were the highest emitters of dioxins in 2017 for Europe, Canada and Australia, when compared to other stationary industrial sources. The change in the trend of dioxin emissions from the iron and steel industry and the public electricity sector was also assessed. The emission of dioxins during 1990–2017 from both iron and steel production and electricity generation revealed a relative decreasing trend, except for Spain and Italy who showed higher level of emissions from iron and steel production in 2017. Furthermore, comparing emission data for metal production revealed that the blast furnace process was the prominent emitter of dioxins comparing to electric arc furnace process. Further investigation was performed to compare the amount of dioxin emitted from three different fuel types, black coal, brown coal and natural gas, used for electricity generation in Australia. The study showed that dioxin emissions from brown coal were higher than black coal for the last two years, while power production from natural gas emits the lowest amounts of dioxins to the environment.

Parameters affecting the formation mechanisms of dioxins in the steel manufacture process

With the implementation of the new national standards in the steel industry, dioxins (polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs)) emission and control have attracted more and more attention in China. The PCDD/Fs levels and signatures of nine steelmaking materials and by-products were experimentally analysed and compared, including five kinds of steelmaking fly ash (sintering fly ash, basic oxygen furnace fly ash, electric arc furnace fly ash and two kinds of blast furnace fly), three kind of steel sludge (continuous casting sludge, hot rolling sludge and cold rolling sludge) and sintering raw material. Dioxin formation from the sintering fly ash was highest of all 9 materials. Furthermore, highly chlorinated PCDD/Fs homologues were abundant in that sample, while the profiles were contrary to those of other materials. More importantly, the entire isomer signatures of all 61 samples were analysed, involving various materials, temperatures, oxygen levels, particle size and inhibitors, with special emphasis on those congeners associated with chlorophenol precursor routes, as well as seventeen 2,3,7,8-substituted PCDD/Fs. Strong correlation was found among seven PCDD-congeners of CP-route. The analysis of the molecular structure of these congeners revealed that 2,4,6/2,3,5-trichlorophenol may act as a precursor to form all those PCDD-congeners by condensation. In addition, the influence of various factors (temperature, oxygen level, particle size, inhibitors addition etc.) on the relative importance of CP-route congeners and 2,3,7,8-substituted congeners was discussed, with the goal of shedding more light on the mechanism of PCDD/Fs-formation.

Synergistic effect of iron and copper oxides on the formation of persistent chlorinated aromatics in iron ore sintering based on in situ XPS analysis

Metal oxides, such as copper (II) oxide (CuO) and iron (III) oxide (Fe₂O₃), are dominant active components in fly ash during iron ore sintering. The potential synergetic effects of these oxides on the formation of chlorobenzenes (CBzs), polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were investigated based on in situ XPS analysis. Besides, the effect of trace metals, such as lead (II) oxide (PbO) and manganese (II) oxide (MnO) (0.5 wt.%), were also studied. The results demonstrated that CuO and Fe₂O₃ showed synergetic effect on the formation of chlorinated aromatics at a Cu/Fe mass ratio of 10:1. The in situ XPS results indicated that the synergistic effect of CuO and Fe₂O₃ with a Cu/Fe mass ratio of 10:1 might be attributed the enhanced oxidation and chlorination of carbon, contributing to a much higher production of CBzs, PCBs and PCDD/Fs. In addition, the quantities of polychlorinated dibenzofurans (PCDFs) were correlated linearly with those of CBzs and PCBs, which suggests the potential of CBzs and PCBs as indicator compounds for predicting PCDD/Fs emissions. Furthermore, the addition of PbO promoted the formation of CBzs while the yield of CBzs and PCBs decreased slightly after addition of MnO to the SFA.

Effects of the addition of municipal solid waste incineration fly ash on the behavior of polychlorinated dibenzo-p-dioxins and furans in the iron ore sintering process

Raw materials were co-sintered with municipal solid waste incineration (MSWI) fly ash through iron ore sintering to promote the safe treatment and utilization of MSWI fly ash. To assess the feasibility of this co-sintering method, in this study, the effects of the addition of MSWI fly ash on the formation and emission of polychlorinated dibenzo-p-dioxins and furans (PCDD/Fs) were estimated via iron ore sintering pot experiments. During co-sintering, most of the PCDD/Fs in the added MSWI fly ash were decomposed and transformed into PCDD/Fs associated with iron sintering, and the concentrations of lower- and mid-chlorinated congeners increased. As there was a sufficient chlorine source and the sintering bed permeability was decreased by the addition of MSWI fly ash, the PCDD/F concentration in the exhaust gas increased. The mass emission of PCDD/Fs decreased; however, the emission of toxic PCDD/Fs increased beyond the total emissions from the independent MSW incineration and iron ore sintering processes due to the transformation of PCDD/F congeners. The co-sintering may be an important solution after technological improvements in the flue gas cleaning system and PCDD/F formation inhibition procedures.

Mechanism of unintentionally produced persistent organic pollutant formation in iron ore sintering

Effects of temperature, carbon content and copper additive on formation of chlorobenzenes (CBzs) and polychlorinated biphenyls (PCBs) in iron ore sintering were investigated. By heating simulated fly ash (SFA) at a temperature range of 250-500°C, the yield of both CBzs and PCBs presented two peaks of 637ng/g-fly ash at 350°C and 1.5×10(5)ng/g-fly ash at 450°C for CBzs, and 74ng/g-fly ash at 300°C and 53ng/g-fly ash at 500°C. Additionally, in the thermal treatment of real fly ash (RFA), yield of PCBs displayed two peak values at 350°C and 500°C, however, yield of CBzs showed only one peak at 400°C. In the thermal treatment of SFA with a carbon content range of 0-20wt% at 300°C, both CBzs and PCBs obtained the maximum productions of 883ng/g-fly ash for CBzs and 127ng/g-fly ash for PCBs at a 5wt% carbon content. Copper additives also affected chlorinated aromatic formation. The catalytic activity of different copper additives followed the orders: CuCl2∙2H2O>>Cu2O>Cu>CuSO4>CuO for CBzs, and CuCl2∙2H2O>>Cu2O>CuO>Cu>CuSO4 for PCBs.

Removal of PCBs and HCB from contaminated solids using a novel successive self-propagated sintering process

Thermal treatments are the primary technologies used to remove persistent organic pollutants from contaminated solids. The high energy consumption during continuous heating, required cost for treating the exhaust gas, and potential formation of secondary pollutants during combustion have prevented their implementation. A novel successive self-propagated sintering process was proposed for removing polychlorinated biphenyls (PCBs) and hexachlorobenzene (HCB) from contaminated solids in a low-cost and environmentally friendly way. Nine laboratory-scale experiments involving different initial concentrations of pollutants and solid compositions were performed. Almost all PCBs (>99%) and HCB (>97%) were removed from solids under constant experimental conditions. Varying initial concentrations of PCBs and HCB in the contaminated solids did not influence the removal efficiency of the pollutants; however, the degradation efficiency of pollutants increased as their initial concentrations increased. Although varying levels of PCDD/Fs were detected in the effluent gas, they were all within the emission standard limit.

Studies into the formation of PBDEs and PBDD/Fs in the iron ore sintering process

Polybrominated diphenyl ethers (PBDEs) and polybrominated dibenzo-p-dioxins and furans (PBDD/Fs) were detected in stack emissions from UK sinter plants. The sum of 36 PBDE congeners was measured at a mean concentration of 295 ng/N m(3) with a standard deviation of 96 ng/N m(3). The mean PBDD/F concentrations were 0.14 ng WHO-TEQ/m(3) (range=0.03-0.39). PBDD/F emission concentrations were approximately ten times lower than their PCDD/F homologues. To understand the possible formation mechanisms of brominated organic species in iron ore sintering, both full-scale and laboratory experiments using an experimental sintering process were carried out. A complete PBDE mass balance was undertaken for a full scale sinter plant showing that PBDEs were already present in the raw materials such as iron ores and coke breeze and that a significant proportion of the PBDE inputs were actually destroyed during the process. A number of controlled experiments were conducted using a laboratory-scale sintering apparatus (sinter pot). These were designed to investigate: (a) mass balance of PBDEs during sintering, (b) the relationship between the availability of bromide (as KBr) and PBDE emissions, and (c) the influence of the availability of both bromide and PBDEs on PBDD/F formation. As observed in the full scale plant, the PBDEs already present in the raw materials were mostly destroyed during the process (79-96%) for all sinter pot experiments. Increasing amounts of KBr in the raw sinter mix did not result in a significant increase in PBDE formation suggesting that there was no PBDE formation in sintering via de novo synthesis. No relationship was observed between PBDE inputs and PBDD/F emissions indicating that PBDEs did not act as precursors for PBDD/Fs formation. Finally, PBDD/F formation was enhanced substantially with increasing amounts of KBr suggesting that their formation mechanism was similar to that of PCDD/Fs via de novo synthesis.

Pyrolysis of MWI fly ash -- effect on dioxin-like congeners

Removal and destruction of dioxin-like congeners, including polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs), from fly ash were investigated at varying pyrolysis temperatures and reaction times and using calcium-based additives. Destruction efficiencies based on TEQ and mass both increase with rising treatment temperature. However, additional low chlorinated PCDD/Fs were formed significantly by dechlorination of high chlorinated PCDD/Fs, at pyrolysis temperatures of 250 and 300°C. Surprisingly, lower destruction efficiencies were realized in the presence of Ca-based additive, compared with those without additive, and TEQ values of fly ash into which CaO was introduced increased, compared with the raw ash, due to significant formation of low chlorinated PCDD/Fs (4-5 Cl). However, complex interactions among unburned carbon, sulfur and metals in the fly ash collected in this study make it difficult to pinpoint the exact causes. The results obtained in this study indicate that degradation and formation of dioxin-like congeners take place simultaneously in pyrolysis process, such as formation of low chlorinated PCDD/Fs via dechlorination of highly chlorinated PCDD/Fs.

Emission characterization of unintentionally produced persistent organic pollutants from iron ore sintering process in China

Emission of unintentionally produced persistent organic pollutants (Unintentional POPs), including polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), polychorinated biphenyls (PCBs), hexachlorobenzene (HxCBz) and pentachlorobenzene (PeCBz), were investigated in four typical iron ore sintering plants in China. The emission factors and annual mass releases of the Unintentional POPs were calculated. The results indicated that PCDFs contributed more than 60% to the overall toxic equivalent quantity (TEQ) values, while the contribution of the dl-PCBs is relatively low, and only in the range of 8-9%. The dominant congeners of PCDD/Fs and dl-PCBs contributing most to the total TEQ were 1,2,3,7,8-PeCDD, 2,3,4,7,8-PeCDF and PCB-126. With regard to the TEQ contributions, the most abundant homologues were PeCDFs and HxCDD/Fs, followed by PeCDDs and non-ortho dl-PCB, whereas HpCDD/Fs, OCDD/Fs and mono-ortho dl-PCBs almost made no contributions. Due to the massive use of recycled waste in the feeding materials, the average emission factor of PCDD/Fs and dl-PCBs of the four plants was 3.95 μg WHO-TEQ ton(-1). Based on the results, the annual release of PCDD/Fs and dl-PCBs in 2007-2009 were estimated to be 2070 g, 2212 g, and 2307 gWHO-TEQ, respectively.

Characteristics of dioxin emissions from a Waelz plant with acid and basic kiln mode

The concentrations of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) were measured in the flue gas of a Waelz plant operated in acid and basic modes, respectively. To abate (PCDD/F) and other pollutants, the plant operates with a post-treatment of flue gases by activated carbon injection and subsequent filtration. Relatively high PCDD/F discharge by fly ashes is found with acid kiln mode of the Waelz process. Therefore, basic kiln mode of the Waelz process is investigated and compared in this plant. With the adsorbent injection rate of 7 kg/h (95 mg/Nm(3)), the PCDD/F concentration in stack gas was measured as 0.123 ng I-TEQ/Nm(3) in the basic operating mode. The added Ca(OH)(2) reacted with metal catalysts and HCl((g)) in the flue gas and thus effectively suppressed the formation of PCDD/Fs. PCDD/F concentrations in fly ashes sampled from the dust settling chamber, cyclone, primary filter and secondary filter in basic kiln mode were significantly lower than that in acid kiln mode. Total PCDD/F emission on the basis of treating one kg of electric arc furnace dust in the basic operation mode was 269 ng I-TEQ/kg EAF-dust treated which was significantly lower than that in acid mode (640 ng I-TEQ/kg EAF-dust treated).

Operating condition influences on PCDD/Fs emissions from sinter pot tests with hot flue gas recycling

This study was designed to clarify the influence of operating conditions on the formation and emissions of polychlorinated-p-dibenzodioxins and dibenzofurans (PCDD/Fs) from a sintering process with hot flue gas recycling. A pilot scale sinter pot with simulated flue gas recycling was developed, and four key operational parameters, including temperature, oxygen content of the simulated waste flue gas, the coke rate of the sintering mixture, and the quicklime quality, were selected for exploring PCDD/Fs formation. The results showed that the temperature of the recycled flue gas had a major affect on PCDD/Fs formation, and a high temperature could significantly increase their formation during sintering. A clear linear correlation between the temperature of recycling flue gas and PCDD/Fs emission (r = 0.93) was found. PCDD/Fs could be reduced to a certain extent by decreasing the level of oxygen in the recycled flue gas, while sintering quality was unchanged. The coke rate had no significant influence on the formation of PCDD/Fs, but the quality of quicklime used in the sintering mixture could affect not only the amount of PCDD/Fs emissions but also the sintering productivity. Compared with a benchmark sinter pot test, PCDD/Fs emissions markedly decreased with improvements to quicklime quality. However, the reduction in PCDD/Fs emissions realized by using high-quality quicklime was limited by the temperature of the inlet gas. The highest reduction achieved was 51% compared with conventional quicklime when the temperature of the inlet gas was 150 degrees C.

Estimation and characterization of PCDD/Fs, dl-PCBs, PCNs, HxCBz and PeCBz emissions from magnesium metallurgy facilities in China

Magnesium production is considered to be one potential source of unintentional persistent organic pollutants (unintentional POPs). However, studies on the emissions of unintentional POPs from magnesium metallurgy are still lacking. Emissions of unintentional POPs, such as polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), polychlorinated naphthalenes (PCNs), hexachlorobenzene (HxCBz) and pentachlorobenzene (PeCBz) are covered under the Stockholm Convention. In this study, these emissions were investigated through a magnesium smelting process. Stack gas and fly ash samples from a typical magnesium plant in China were collected and analyzed to estimate the emissions of unintentional POPs from magnesium metallurgy. Emissions factors of 412 ng TEQ t(-1) for PCDD/Fs, 18.6 ng TEQ t(-1) for dl-PCBs, 3329 μg t(-1) for PCNs, 820 μg t(-1) for HxCBz, and 1326 μg t(-1) for PeCBz were obtained in 2009. Annual emissions from magnesium metallurgy in China were estimated to be 0.46 g WHO-TEQ for PCDD/Fs and dl-PCBs, 1651 g for PCNs, 403 g for HxCBz and 653 g for PeCBz, respectively.

Formation and mitigation of PCDD/Fs in iron ore sintering

The sintering of iron ore is presently a significant industrial source of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) worldwide owing to the fundamental requirement of the operation of a high temperature process to pre-treat fines and to recycle plant by-products arising from the integrated iron and steelworks. The process is a noteworthy contributor of PCDD/F indirectly due to decreasing PCDD/F releases from municipal solid waste incineration. Commonly PCDD/F formation from the process is associated with the addition of oily mill scales although raw material containing a combination of C, Cl and specific metal catalyst has been shown to drastically increase PCDD/F formation in the process. The degenerate graphitic structure of carbon present in coke fuel and soot formed and the chemistry of catalytic metals and Cl are important factors. A review on PCDD/F emission in this process has been carried out, including examination of its formation mechanism, congener distribution, contributing factors and mitigation strategies, with emphasis on the use of inhibiting compound to achieve suppression. A detailed analysis of the de novo and precursor theories of formation and the contributing factor is given since the subject of PCDD/F formation is still controversial. The de novo formation pathway identified in sinter plants and controlled studies performed in the laboratory as well as at pilot-scale are discussed; where appropriate, a comparison is drawn between sintering and other thermal processes emitting PCDD/Fs. Summary of the latest developments in PCDD/F downstream abatement strategies presently employed in full scale industrial plants is provided. Potential inhibiting compounds are discussed in terms of their mode of action and merits under sintering conditions.

Removal of chloride from electric arc furnace dust

Electric arc furnace (EAF) dust with high chloride content increases the threat of dioxin emissions and the high chloride content reduces the value of recycled zinc oxide produced by EAF dust recycling plants. This study conducts a number of laboratory experiments to determine the technical feasibility of a new dechlorination method. These methods consist of a series of roasting processes and water washing processes. In the roasting process, EAF dust was heated in a tube furnace to evaluate the parameters of atmospheric conditions, roasting temperature, and roasting time. Results indicate that sulfation roasting is more efficient in reducing chloride content than other roasting processes. The water washing process can totally remove water-soluble chloride at a solid to liquid ratio of 1:10. However, the remaining water-insoluble substance is difficult to dechlorinate. For example, lead chloride forms a hydroxyl-halide (PbOHCl) and lead chloride carbonate (Pb(2)CO(3)Cl(2)) agglutinative matrix that is hard to wash away.

Degradation of gaseous dioxin-like compounds with dielectric barrier discharges

Developing effective technologies to reduce dioxin emissions has become an important issue in the research and industrial fields. In this study, a dioxin-containing gas stream generating system was applied to evaluate the effectiveness of dielectric barrier discharge (DBD) plasma technology for the destruction of dioxin-like compounds. The results indicate that the destruction efficiencies of dioxin-like compounds achieved with DBD plasma strongly depend on the composition of the simulated gas stream. As the DBD plasma is operated with the simulated gas stream containing 20% water vapor, around 74% PCDDs and 89% PCDFs can be destroyed by DBD plasma. UV, electrons, and OH radicals are generated via the DBD plasma process and react with the dioxin-like compounds in the gas stream. Dechlorination via UV and electrons and decomposition via OH radicals occur at the same time and significantly increase the destruction efficiency of PCDD/Fs in the presence of oxygen and water vapor. Additionally, the total toxicity destruction of dioxin-like compounds with the input energy of 1 kJ increases from 1.47 to 3.06 ng-TEQ(WHO) as the water vapor is incorporated into the gas stream.

Distribution of polycyclic aromatic hydrocarbons and polychlorinated dibenzo-p-dioxins/dibenzofurans in ash from different units in a municipal solid waste incinerator

Polycyclic aromatic hydrocarbons (PAHs), polychlorinated-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are some of the major organic contaminants emitted in municipal solid waste incinerators (MSWIs). The distribution of PAHs and PCDD/Fs in different MSWI unit ashes, including bottom residue (BR), fly ash pit (FAP), fabric filter (FF), semi-dryer absorber (SDA), economizer (EC) and super heater (SH), has seldom been discussed. Average PAHs content in ash samples from BR, FAP, FF, SDA, EC and SH were found to be 0.020, 0.237, 0.234, 0.125, 0.037 and 0.034 µg TEQ g(-1), respectively. In addition, the range of total emission factor from different unit ashes varied between 0.30-13.85 mg TEQ tonne(-1) of waste, low molecular weight compounds (2~3-ring) being the dominant species. Furthermore, PAHs in ashes were mainly found in BR (41%) and FAP (31%). The FAP ash included 18% of PAHs coming from FF ash. On the other hand, PCDD/Fs content in BR, FAP, FF, SDA, EC and SH was found to be 0.0329, 1.1589, 1.2807, 0.1476, 0.6868 and 0.0921 ng I-TEQ g(-1), respectively. PCDD/ Fs emission factors in this study ranged between 1.029-67.740 µg I-TEQ tonne(-1) of waste, most PCDD/Fs being present in FAP (55%). The FAP ash included 33% of PCDD/Fs coming from FF ash. Therefore, PCDD/Fs content in FAP and FF exceeded the legal limit of 1 ng I-TEQ g( -1); therefore, a solidification process is necessary before landfilling in Taiwan.

Experimental study on the effects of H(2)O on PCDD/Fs formation by de novo synthesis in carbon/CuCl(2) model system

The effects of H(2)O vapor on de novo synthesis of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and biphenyls (PCB) were investigated at two levels (none and 10 vol.%) in various model systems containing five different carbons, CuCl(2), and quartz, exposed to a flow of 10% O(2)/N(2) at 300 degrees Celsius. The influence of H(2)O was studied on (1) speciation and behavior of copper compounds, (2) catalytic oxidation of carbons of distinct reactivity, and (3) formation of organic chlorine compounds, with the aim to investigate any effects on de novo synthesis. It is found that H(2)O converts CuCl(2) to CuCl(2) x CuO, and finally to CuO in a flow of 10% O(2)/N(2) at 300 degrees Celsius and that it decreases of organic chlorine (C-Cl) formation. When CuCl(2) is supported on carbon, the addition of H(2)O promotes the catalytic oxidation of this carbon. When CuCl(2) is supported on quartz, however, H(2)O inhibits carbon oxidation. A decrease in chlorination level of PCDD/Fs and PCBs with water addition is observed for all (six) model ashes; yet this addition affects the yields of PCDD/Fs and PCBs differently. Under the experimental conditions tested H(2)O does not react with Cu(2)Cl(2), which is the catalyst of carbon oxidation. On the basis of the experimental results, the following mechanism is proposed: conversion of CuCl(2) into CuO which is less reactive in de novo synthesis and promotion of catalytic oxidation of carbon by Cu(2)Cl(2).

Atmospheric emission of PCDD/Fs, PCBs, hexachlorobenzene, and pentachlorobenzene from the coking industry

The coking process is considered to be a potential source of unintentionally produced persistent organic pollutants (UP-POPs). However, intensive studies on the emission of UP-POPs from the coking industry are still very scarce. Emission of polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs), dioxin-like polychlorinated biphenyls (dl-PCBs), hexachlorobenzene (HxCBz), and pentachlorobenzene (PeCBz) covered under the Stockholm Convention were investigated for the coking process in this study. Stack gases from some typical coke plants in China were collected and analyzed to estimate the emission of UP-POPs from the coking industry. Emission factors of 28.9 ng WHO-TEQ tonne(-1) for PCDD/Fs, 1.7 ng WHO-TEQ tonne(-1) for dl-PCBs, 596 ng tonne(-1) for HxCBz, and 680 ng tonne(-1) for PeCBz were derived based on the investigated data. The annual emissions from the global coking industry were estimated to be 15.8 g WHO-TEQ for PCDD/Fs, 0.93 g WHO-TEQ for dl-PCBs, 333 g for HxCBz, and 379 g for PeCBz, respectively (reference year 2007). According to the distribution of PCDD/Fs, we argued for the de novo synthesis to be the major pathway of PCDD/F formation. With regard to the characteristics of dl-PCBs, the most abundant congener was CB-118, and the most dominant contributor to the total WHO-TEQ of dl-PCBs was CB-126.

Potential formation of PCDD/Fs and related bromine-substituted compounds from heating processes for ashes

Thermal experiments were conducted using real boiler ash and fly ash samples from three types of municipal or industrial solid waste incineration plants to understand the formation reactions of polychlorinated dibenzo-p-dioxin and furans (PCDD/Fs) and related bromine compounds that were chlorinated-brominated dibenzodioxins and furans (PXDD/Fs) and polybrominated dibenzo-p-dioxin and furans (PBDD/Fs). The results obtained were as follows: The formation of PCDD/Fs was clearly shown, and fly ash containing abundant carbon matter had a significant potential for de novo synthesis. The homologous distribution change apparently showed that the formation of PXDD/Fs occurred from the substitution of a bromine atom with a chlorine atom in the PCDD/F molecules. This suggests that PXDD/Fs are usually formed with PCDD/Fs on the ash. PBDD/Fs might be formed from any reaction mechanism different from that of PXDD/Fs. The existence of carbonaceous matters always does not mean the potential formation of PCDD/Fs. However, any addition of catalytic copper may influence the nature of ash to increase the formation potential. The findings suggest that there are many instances that result in the unintended production of trace hazardous pollutants in the incineration process and show that careful and sophisticated control is required to prevent the formation of pollutants.

Characteristics and emission factors of PCDD/Fs in various industrial wastes in South Korea

Since South Korea ratified Stockholm Convention in January 2007, there is an obligation to survey the national emission of PCDD/Fs through environmental routes other than the air for taking actions to reduce and/or eliminate the release of PCDD/Fs. In this study, PCDD/F-containing wastes from various industrial emission sources in Korea (n=388) except from incinerators were investigated to elucidate the emission characteristics and their emission factors of PCDD/Fs in each industry. The concentrations of PCDD/Fs in waste samples ranged ND-96,200 ng I-TEQ kg(-1) (or 66,600 ng WHO-TEQ kg(-1)) for solid phase samples and ND-11,100 pg I-TEQL(-1) (or 6800 ng WHO-TEQ L) for liquid samples, respectively. Elevated levels of PCDD/F concentrations and emission factors were found in the wastes from productions of Cu, Al, Zn, Iron/steel, Pb, EDC/VCM/PVC and from waste landfill sites. The wastes from productions of cement (kilns) and acetylene (carbide method) showed elevated levels of PCDD/F emission factors only. The dominant congeners were OCDD, OCDF, 1,2,3,4,6,7,8-HpCDF and 1,2,3,4,5,7,8-HpCDD. The PCDF ratios in samples from thermal processes and solid phase samples were 69% and 70%, respectively. The ratio of OCDD congener (about 23.5%) was higher than that of other congeners in both solid and liquid phase wastes. These results can be used as a useful reference for the establishment of the PCDD/F inventory and their management plans.

Determining optimal operation parameters for reducing PCDD/F emissions (I-TEQ values) from the iron ore sintering process by using the Taguchi experimental design

This study is the first one using the Taguchi experimental design to identify the optimal operating condition for reducing polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/ Fs) formations during the iron ore sintering process. Four operating parameters, including the water content (Wc; range = 6.0-7.0 wt %), suction pressure (Ps; range = 1000-1400 mmH2O), bed height (Hb; range = 500-600 mm), and type of hearth layer (including sinter, hematite, and limonite), were selected for conducting experiments in a pilot scale sinter pot to simulate various sintering operating conditions of a real-scale sinter plant We found that the resultant optimal combination (Wc = 6.5 wt%, Hb = 500 mm, Ps = 1000 mmH2O, and hearth layer = hematite) could decrease the emission factor of total PCDD/Fs (total EF(PCDD/Fs)) up to 62.8% by reference to the current operating condition of the real-scale sinter plant (Wc = 6.5 wt %, Hb = 550 mm, Ps = 1200 mmH2O, and hearth layer = sinter). Through the ANOVA analysis, we found that Wc was the most significant parameter in determining total EF(PCDD/Fs (accounting for 74.7% of the total contribution of the four selected parameters). The resultant optimal combination could also enhance slightly in both sinter productivity and sinter strength (30.3 t/m2/day and 72.4%, respectively) by reference to those obtained from the reference operating condition (29.9 t/m (2)/day and 72.2%, respectively). The above results further ensure the applicability of the obtained optimal combination for the real-scale sinter production without interfering its sinter productivity and sinter strength.

Reduction of dioxin-like compound emissions from a Waelz plant with adsorbent injection and a dual baghouse filter system

Previous study indicates that the polychlorinated dibenzo-p-dioxin and -dibenzofurans (PCDD/F) concentration measured in the stack gas of the Waelz plant investigated reached 194 ng-TEQ/(N m3) (TEQ = toxic equivalence), due to the relatively high potential of PCDD/F formation and a low PCDD/F removal efficiency (<70%) achieved with the baghouse filter (BF). In September 2006, the Taiwan government setthe PCDD/F emission limit for existing Waelz plants as 1.0 ng-I-TEQO/(N m3). The retrofit technology for reducing PCDD/F emissions from the existing Waelz plant was evaluated at the same time. Carbon-type adsorbent injection technology was adopted in early 2006 to reduce the emission of dioxin-like compounds at the Waelz plant investigated. Flue gases and ambient air samplings were conducted during the two stages of retrofit to evaluate the removal efficiency of dioxin-like compounds at the Waelz plant investigated. At stage 1, by applying adsorbent injection + single baghouse filter (SBF), the PCDD/F and polychlorinated biphenyl (PCB) concentrations measured in the stack gas at the Waelz plant were 4.62 ng-TEQ/(N m3) and 0.08 ng-TEQ(WHO)/(N m3) (TEQ(WHO) = World Health Organization TEQ), respectively, as the adsorbent injection rate was controlled at 40 kg/h (or 540 mg/ (N m3)). At stage 2, the PCDD/F and PCB concentration measured at stack gas, achieved with adsorbent injection + dual baghouse filter (DBF) system, were further reduced to 0.235 + 0.04 ng-I-TEQ/(N m3) (I-TEQ = International TEQ) and 0.004 + 0.002 ng-TEQ(WHO)/(N m3) with the adsorbent injection rate at 16 kg/h (or 215 mg/(N m3)). In the meantime, the atmospheric PCDD/F concentrations measured in the vicinity area of the Waelz plant were greatly reduced from 568-1465 to 48.9-130 fg-I-TEQ/m3. Higher removal efficiency (>99.8%) achieved at a lower adsorbent injection rate (16 kg/h) of the adsorbent injection + DBF system also significantly reduced the total PCDD/-F and PCB emission flows (per kg of electric arc furnace dust treated) to 1925 ng-I-TEQ and 30.5 ng-TEQ(WHO), respectively.

Measurement of atmospheric PCDD/F and PCB distributions in the vicinity area of Waelz plant during different operating stages

A comprehensive sampling program was conducted at four sampling sites in the vicinity area of a Waelz plant prior to and after the retrofitting of this plant for reducing PCDD/F (polychlorinated dibenzo-p-dioxin and polychlorinated dibenzofuran) and polychlorinated biphenyl (PCB) emission to evaluate its effects on atmospheric PCDD/F and PCB concentrations. During the shutdown stage of the Waelz plant investigated, the atmospheric PCDD/F and PCB concentrations measured in the vicinity area (sites A, B and C) range from 24 to 170 fg-I-TEQ/m(3) and 5.0 to 8.2 fg-TEQ(WHO)/m(3), respectively. As the facility restarted to operate, the atmospheric PCDD/F and PCB concentrations measured increased to 570-1460 fg-I-TEQ/m(3) and 23-59 fg-TEQ(WHO)/m(3), respectively. When activated carbon injection (ACI) was adopted in the facility in early 2006, the PCDD/F concentrations measured in stack gas decreased dramatically from 190 to 3.4 ng-I-TEQ/Nm(3), while the PCB concentrations decreased from 4.9 to 0.08 ng-TEQ(WHO)/Nm(3). In the meantime, the atmospheric PCDD/F and PCB concentrations measured at sites A, B and C decreased to 150-340 fg-I-TEQ/m(3) and 13-19 fg-TEQ(WHO)/m(3), respectively. However, relatively high PCDD/F (180-1460 fg-I-TEQ/m(3)) and PCB (9.3-59 fg-TEQ(WHO)/m(3)) concentrations were measured at site D during all sampling stages. Overall, atmospheric sampling results indicate that over 50% of PCDD/Fs distributed in solid phase, while over 90% of PCBs distributed in vapor phase during all sampling stages.

Role of temperature and hydrochloric acid on the formation of chlorinated hydrocarbons and polycyclic aromatic hydrocarbons during combustion of paraffin powder, polymers, and newspaper

Formation of chlorinated hydrocarbons and polycyclic aromatic hydrocarbons (PAHs) were determined using a laboratory-scale incinerator when combusting materials at different temperatures, different concentrations of hydrochloric acid (HCl), and when combusting various types of polymers/newspaper. Polychlorobenzenes (PCBz), polychlorophenols (PCPhs), polychlorinated dibenzo-p-dioxins/furans (PCDD/Fs) and their toxic equivalency (TEQ) and PAHs were highlighted and reported. Our results imply maximum formation of chlorinated hydrocarbons at 400 degrees C in the following order; PCBz>or=PCPhs>>PCDFs>PCDDs>TEQ on a parts-per-billion level. Similarly, a maximum concentration of chlorinated hydrocarbons was noticed with an HCl concentration at 1000 ppm with the presence of paraffin powder in the following order; PAHs>PCBz>or=PCPhs>>PCDFs>PCDDs>TEQ an a parts-per-billion level. PAHs were not measured at different temperatures. Elevated PAHs were noticed with different HCl concentrations and paraffin powder combustion (range: 27-32 microg/g). While, different polymers and newspaper combusted, nylon and acrylonitrile butadiene styrene (ABS) produced the maximum hydrogen cyanide (HCN) concentration, concentrations of PCDD/FS, dioxin-like polychlorinated biphenyls (DL-PCBs), and TEQ were in a decreasing order: polyvinylchloride (PVC)<newspaper<polyethyleneterephthalate (PET)< polyethylene (PE)< polypropylene (PP)< ABS = blank. Precursors of PCBs were in a decreasing order: PP<nylon<PE<newspaper<ABS<PVC<blank<PET. Precursors of PCDD/Fs were in a decreasing order: newspaper <PP=nylon<PE<ABS<PVC= blank<PET. BTX formation was in a decreasing order; PE<nylon<newspaper<ABS<PP. PAHs formation were elevated with parts-per-million levels in the decreasing order of PP<nylon<PE<newspaper<blank<ABS< PET<PVC.

PCDD/F and "Dioxin-like" PCB emissions from iron ore sintering plants in the UK

Investigations have been carried out at the three Corus UK sinter plants over the period 2002-2004 to characterise the emissions of both 2,3,7,8-PCDD/Fs and WHO-12 PCBs, to estimate annual mass releases of these organic micro-pollutants using the I-TEF and WHO-TEF schemes, and to investigate the formation of PCBs in the iron ore sintering process. Results showed that the sintering of iron ore produces a characteristic WHO-12 PCB and PCDD/F congener pattern that is substantially the same for all UK sinter plants. With regard to WHO-12 PCBs, the most abundant congeners were typically PCBs 118 (6-9 ngNm(-3)), 105 (2-4 ngNm(-3)) and 77 (2-3 ngNm(-3)). All other WHO-12 PCBs were also detected at concentrations around 1 ngNm(-3). All sinter plants investigated exhibited very similar TEQ concentrations. WHO-12 PCB emissions were in the range 0.042-0.111 ngWHO-TEQNm(-3), whereas PCDD/F emissions ranged from 0.39 to 1.62 ngWHO-TEQNm(-3). PCDF congeners were the main contributors to the overall TEQ in sintering emissions (ca. 85%). Amongst WHO-12 PCBs, PCB 126 was the only noteworthy contributor to total TEQ (ca. 5-7%), a similar contribution to that from PCDDs. Based on the measurements that Corus UK has undertaken at these three sinter plants, annual mass releases of WHO-12 PCBs and PCDD/Fs have been calculated. For UK sinter plants, a total mass release of 29.5 g WHO-TEQ per annum [WHO-12 PCBs+PCDD/Fs] has been estimated, representing 9% of the total PCDD/F emissions to the UK atmosphere. Measurements were also carried out at a UK sinter plant to determine the windleg emission profile of WHO-12 PCBs. Results showed that WHO-12 PCBs were formed in the same regions of the sinter strand as 2,3,7,8-PCDD/Fs, indicating that there was a strong correlation between the formation of WHO-12 PCBs and PCDD/Fs in the iron ore sintering process.

Effect of water on catalyzed de novo formation of polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans

The effect of water vapor on catalyzed de novo formation of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF) was investigated through experiments conducted on a fixed-bed apparatus. The results indicated that water vapor could promote the formation of PCDD and PCDF. The dominant pathway was activating fly ash in this work, while water also reacted with chlorine to change the equilibrium of Deacon reaction, which influenced the final yield of PCDD/PCDF. Also a suppression effect of water on CuCl(2) was found according to the values of the catalysis indicator. It is possible that water reduced the catalysis of CuCl(2) or prevented its direct chlorination. But the overall effect of water on the formation of PCDD and PCDF was promotion rather than inhibition.

Partitioning and removal of dioxin-like congeners in flue gases treated with activated carbon adsorption

Activated carbon adsorption is commonly used to control dioxin-like congener (PCDD/Fs and PCBs) emissions. Partitioning of PCDD/Fs and PCBs between vapor and solid phases and their removal efficiencies achieved with existing air pollution control devices (APCDs) at a large-scale municipal waste incinerator (MWI) and an industrial waste incinerator (IWI) are evaluated via intensive stack sampling and analysis. Those two facilities investigated are equipped with activated carbon injection (ACI) with bag filter (BF) and fixed activated carbon bed (FACB) as major PCDD/F control devices, respectively. Average PCDD/F and PCB concentrations of stack gas with ACI+BF as APCDs are 0.031 and 0.006ng-TEQ/Nm(3), and that achieved with FACB are 1.74 and 0.19ng-TEQ/Nm(3) in MWI and IWI, respectively. The results show that FACB could reduce vapor-phase PCDD/Fs and PCBs concentrations in flue gas, while the ACI+BF can effectively adsorb the vapor-phase dioxin-like congener and collect the solid-phase PCDD/Fs and PCBs in the meantime. Additionally, the results of the pilot-scale adsorption system (PAS) experimentation indicate that each gram activated carbon adsorbs 105-115ng-PCDD/Fs and each surface area (m(2)) of activated carbon adsorbs 10-25ng-PCDD/Fs. Based on the results of PAS experimentation, this study confirms that the surface area of mesopore+macropore (20-200A) of the activated carbon is a critical factor affecting PCDD/F adsorption capacity.

Characteristics of PCDD/F distributions in vapor and solid phases and emissions from the Waelz process

The Waelz process is a classic method used for recovering zinc from electric arc furnace (EAF) dusts containing relatively high concentrations of PCDD/Fs (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) as well as volatile metals, such as Zn, Pb, and Cu, and chlorine. As a result of the operating temperature in the cooling process and high carbon and chlorine contents, significant PCDD/Fs are formed in the typical Waelz process, causing public concerns regarding PCDD/F emissions. In this study, flue gas and ash samplings are simultaneously conducted at different sampling points to evaluate the removal efficiency and the partitioning of PCDD/Fs between the vapor and solid phases in the Waelz plant investigated. With the environment (temperature window, sufficient retention time, chlorine, and catalysts available) conducive to PCDD/F formation in the dust settling chamber (DSC), a significantly high PCDD/F concentration (1223 ng TEQ/Nm3) is measured in flue gas downstream from the DSC of the Waelz plant investigated. In addition, the cyclone and bag filter adopted in this facility can only remove 51.3% and 69.4%, respectively, of the PCDD/Fs in the flue gas, resulting in a high PCDD/F concentration (145 ng TEQ/Nm3) measured in the stack gas of the Waelz plant investigated. On the basis of treating 1 ton of EAF dust, the total PCDD/F discharge (stack gas emission + ash discharge) is 840 ng TEQ/kg EAF dust of the Waelz plant investigated. Because of the lack of effective air pollutant control devices for PCDD/Fs, about 560 ng TEQ/kg EAF dust are discharged via stack gas in this facility.

Evaluation of PCDD/F congener partition in vapor/solid phases of waste incinerator flue gases

Activated carbon injection (ACI) is commonly used to control PCDD/F (polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans) emissions from stationary sources. In this study, the characteristics of PCDD/Fs emitted from one municipal waste incinerator (MWI) and two industrial waste incinerators (IWI-1 and IWI-2) that apply activated carbon systems for controlling the emissions are investigated via intensive stack sampling. MWI and IWI-1 are equipped with ACI and bag filters (BF) while IWI-2 is equipped with a fixed activated carbon bed (FCB). Results indicate that most PCDD/Fs in flue gas downstream of ACI+BF exist in vapor phase (over 90%) while most PCDD/ Fs exist in solid phase (over 60%) downstream of FCB. For MWI and IWI-1, the removal efficiencies of vapor and solid-phase PCDD/Fs are 98.5-99.6% and 99.8-99.9%, respectively. In addition,the removal efficiencies of vapor- and solid-phase PCDD/Fs are 84.5% and -13.4% in IWI-2, respectively. The results also indicate that the partition of vapor/solid-phase PCDD/F is affected by the type of the air pollutant control devices (APCDs) applied upstream and the particulate matter concentration in flue gas. On the basis of the sampling results of waste incinerators, this study preliminarily establishes the equations for predicting vapor/solid-phase PCDD/F partition in flue gases downstream of various APCDs including cyclone (CY), electrostatic precipitator (EP), FCB, ACI+BF, and selective catalytic reduction system (SCR).